Gear Rattle during a start-up transient in a driveline equipped with a tuneable torsional Vibration Damper with Magneto-Rheological Elastomers

The paper reports a numerical investigation on the dynamic behaviour of a vehicle driveline, equipped with a Torsional Vibration Damper (TVD) based on Magneto-Rheological Elastomeric (MRE) spring elements, during the start-up transient considering an abrupt manoeuvre of clutch engagement. The TVD device consists of a flywheel and a damper disk, with interposed some elastomeric samples which react for relative angular displacements of the two disks. The dynamical parameters of the TVD can be properly tuned by varying the magnetic field surrounding the MRE springs to mitigate the torsional oscillations of the flywheel, causes of many undesired inconveniences as critical speeds or vibro-acoustic issues. The present study promotes the use of the MRE torsional vibration damper to reduce the annoying vibroacoustic phenomenon of “gear rattle” arising in the unloaded gear pairs of the gear box, during and after the rapid clutch engagement transients in the vehicle start-up phase and is conducted on a simplified automotive driveline equipped with a dry clutch. The possibility of quickly tuning the mechanical properties of the MRE-TVD, makes this device particularly eligible for suppressing the above disturbance, adapting to the various operative conditions of the automotive driveline. Results of the analysis, by the help of a Gear Rattle Index (GRI), demonstrate the effectiveness of the proposed device in reducing the vibroacoustic phenomenon during the transient phases of the vehicle start-up, until the vehicles speed conditions are reached.

Thermal and Mechanical Analyses of Dry Clutch Disk made of Functionally Graded Material.

This paper presents an innovative utility of Functionally Graded Aluminum Matrix Composite (FGAMC) with Silicon Carbide as a friction material in clutches since having an acceptable friction coefficient and high wear resistance. FGAMC’s properties were calculated using rule-of-mixture and power law, represented by layered geometry. FGAMC’s behavior is examined considering statics, dynamics, thermal and wear. Analyses were done using Finite Element method, by ANSYS. Results are discussed by comparing FGAMC’s clutch to Aluminum matrix composite with 20% of Silicon Carbide clutch and E-glass clutch. Clutches design based on the common size and working conditions of clutches in mid-size and heavy automobiles. Most analyses revels FGAMC’s clutch has higher strain than AMC’s clutch with less deformation in thickness direction and less stresses. FGAMC’s clutch has higher mass leading to lower first natural frequency but with low resulted deformations. Transient analyses showed 10 times fewer maximum deformations for FGAMC’s clutch than AMC and E-glass with lower strains and higher stress but in much less area for FGAMC’s clutch. Wear which indicates working life of a clutch, have been studied using Archard Wear Equation in ANSYS, FGAMC’s clutch has 10 times lower wear with much less affected area compared to AMC and E-glass. Thermal analysis results of the three clutches are close to each other with 0.07 watts between FGAMC’s and AMC’s clutches, and 0.03 watts between FGAMC’s and E-Glass’s clutches.

SIMULATION OF A DUAL CLUTCH AUTOMATED TRANSMISSION GEAR SHIFT

A computer dynamic model of an automobile transmission with a double dry clutch, created using the "Universal Mechanism" software package, is presented. Work objective is to analyze the possibility of improving double dry clutch efficiency at various controls of compressive forces of clutch plates. The computer model contains 7 bodies: an engine crankshaft, two clutch plates, two gearbox input shafts for odd and even gears, an output shaft, a fly wheel. The simulation of gear shifting shows that pressing a clutch pedal or letting out the clutch simultaneously, cutoff time increment increases the rotational speed justification of the engine shaft and the input shaft of the actual gear, the total work of the friction forces of both clutches and does not affect the maximum value of clutch plates rotary sliding resistance. Frictional energy of the clutch when shifting gears from lower to higher is greater than when shifting gears from higher to lower. Sequential clutch on-off reduces the total frictional energy of both clutches by 1.17...1.31 times compared to simultaneous one. The model allows looking into different gearshift modes with uniform velocity or accelerated vehicle motion, optimize the gearshift strategy.

Performance verification test of coaxial centrifugal clutch for motorcycle transmission system

With the popularization of motorcycles, the demand for motorcycles is getting higher and higher. Therefore, the improvement of power output, the reduction of pollutants discharged, the replacement of waste, the improvement of efficiency and the reduction of fuel use, are also relatively important. Stop-and-go on urban driving will keep the clutch in a state of being engaged and not engaged. The clutch cannot be engaged and is constantly worn. The output efficiency of the CVT belt-type continuously variable transmission system clutch used in the transmission is only about 70~80%. Transmission efficiency. Furthermore, since the traditional CVT belt-type system clutch mainly relies on the action of the centrifugal roller to change the reduction ratio, when encountering different driving conditions and need to accelerate and decelerate, this will make the working area of the internal combustion engine in an unstable state. The matching structure between the automatic clutch weight and the telescopic spring in the reciprocating separation state and the fitted state is replaced, which effectively reduces the problem of uneven contact surfaces of the plates in the past, and prevents the elastic aging from affecting the uniform transmission of power, resulting in the entire dry clutch The life span of the engine is improved and the efficiency of power transmission is maintained, thereby reducing fuel consumption and producing more complete engine power. Therefore, the “Design Performance Verification of Coaxial Contact Centrifugal Ball Clutch” is proposed mainly to verify that the coaxial contact centrifugal ball clutch has better performance than the CVT belt-type clutch.

Analysis of the Accuracy of Mass Difference-Based Measurement of Dry Clutch Friction Material Wear

The paper demonstrates that the dry clutch friction plate wear rate, measured based on the plate mass difference method, exhibits a transient behavior after each change of friction interface temperature level. The effect is hypothesized to be caused by a temperature-dependent change in the moisture content/mass level in the friction material. To test this hypothesis, a series of synchronized characterization experiments have been conducted by using two friction plates, one for wear tests and the other for drying in an oven under the same temperature conditions. Based on the analysis of test results, a moisture content compensation procedure, which reduces the transient wear rate from being 100% to being 50% higher compared to stabilized wear rate, is proposed and verified. The gained insights are used to set recommendations on the organization of routine wear characterization experiments aimed at avoiding the effect of moisture content influence on the accuracy of wear measurement. The main recommendations are to minimize the number of temperature target level changes through proper design of the experiment, insert a run-in test after every long test pause, and execute a pre-heat, blind wear test at the beginning of each test day.

Automotive dry clutch fully coupled transient tribodynamics

Determining the root causes of Noise, Vibration and Harshness (NVH) phenomena in modern automotive drivetrains is a task of critical importance. This research investigates the stability of dry clutch systems vibrational behaviour during engagement. A fully coupled dry clutch numerical model including the influence of friction is presented and validated using vehicle measurements. The clutch component frictional properties are measured using parts that exhibit aggressive NVH behaviour using representative tribometric experiments. The validated numerical tool highlights the occurrence of instabilities which are caused by modal couplings, particularly between the input shaft bending and clutch disc radial motions. Such a validated transient dynamics model of a dry clutch system has not hitherto been presented in the open literature.

Effects of vehicle driveline parameters and clutch judder on gearbox vibrations

Clutch judder causes discomfort in a car. This undesirable event not only creates noise and vibrations, it also disturbs the normal functionality of other components in the driveline, especially the gearbox, which is prone to oscillating inputs. Although there are numerous separate studies on clutch judder and gearbox vibrations, a combined study is necessary in order to investigate the coupled dynamics, especially the effect of vibrations in a clutch on gearbox vibrations. In this paper, a dynamic model is presented for the driveline, including the details of a gearbox and a dry clutch. It allows us to investigate the effect of clutch parameters and to simulate conditions with and without judder. The obtained dynamical equations are then solved numerically. The influence of judder on gear dynamics and passenger comfort is investigated. The results show that judder causes loss of contact in the gearbox in most cases. In more severe cases of judder, it can cause rattle not only in the unloaded gear, but also in the loaded gears. A modal analysis and a frequency spectrum analysis are conducted as well in order to identify the frequency components of the system vibrations and to verify the obtained results. Parts of the results are compared with the theoretical and experimental data from other research studies, which show agreement and serve to validate the model in this work.